The present invention relates to an electronic heat pump device for performing, for example, conversion from electric energy to heat energy (electric to thermal energy conversion), and more specifically, relates to an electronic heat pump device in which a distance between an emitter and a collector is approximated to a nano-level distance, and a voltage is applied so as to emit electrons from the emitter side with use of electron tunneling, thereby cooling one-side surface of the apparatus while heating the other-side surface without the necessity of refrigerants and compressors and without a mechanical operation section. The present invention further relates to electronic equipment utilizing the electronic heat pump device and a method of manufacturing the electronic heat pump device.
Conventional electronic heat pump devices are typified by peltiert devices. The peltiert device is an electronic heat pump device which has, as shown in FIG. 37, a p-type semiconductor 51, an n-type semiconductor 52 and metal electrodes 53 and uses Peltier effect. In the peltiert device, voltage application and current feeding cause heat absorption or heat generation between each of the semiconductors 51, 52 and the electrodes 53, so that heat is traveled from an endothermic portion to an exothermic portion.
Moreover, as shown in FIG. 38, electronic heat pump devices different in structure from the peltiert devices are vacuum diode-type electronic heat pump devices having a vacuum gap 63 formed between an emitter 61 and a collector 62, and their concrete examples include the following first to fourth electronic heat pump devices.
As shown in FIG. 39, the first electronic heat pump device is structured such that a cathode 71 (equivalent to an emitter) which is thermally connected to a cooling target and an anode 72 (equivalent to a collector) which is thermally connected to a heating target face to each other with a vacuum gap (vacuum atmosphere) 73 interposed therebetween, and a voltage is applied to between electrodes 71a and 72a to feed current (see U.S. Pat. No. 5,675,972).
The cathode electrode 71a and the anode electrode 72a are formed from a material having a low work function such as complexes made of alkali metal, and the work function of the cathode electrode 71a is lower than the work function of the anode electrode 72a. Causing a temperature difference between the cathode 71 and the anode 72 generates an electron flow from the cathode electrode 71a to the anode electrode 72a. 
The term “work function” herein refers to a physical property value representing an electron emission capability of a given material in the case where with certain energy (e.g., heat or electric field) applied to the material, electrons are extracted from the surface of the material beyond an external energy barrier (e.g., vacuum). A lower work function signifies a larger electron emission amount.
As shown in FIG. 40, the second electronic heat pump device has an emitter 81 connected to a first thermal conduction section 84, and a collector 82 connected to a second thermal conduction section 85 through a piezoelectric element 86 (see International Publication No. WO99/13562).
The vacuum gap 83 between the emitter 81 and the collector 82 is maintained to be a specified space by expanding or shrinking the piezoelectric element 86 through electric control while capacitance between the emitter 81 and the collector 82 is being regulated.
As shown in FIG. 41, the third electronic heat pump device has an emitter 81 connected to a first thermal conduction section 84 and a collector 82 connected to a second thermal conduction section 85 through a piezoelectric element 86 (see U.S. Pat. No. 6,417,060 B2).
Capacitance between the emitter 81 and the collector 82 is read at any time and the data is processed in a piezo feedback circuit 87, after which the piezoelectric element 86 is expanded or shrunk so as to maintain the vacuum gap 83 between the emitter 81 and the collector 82 to be a specified distance.
Further, in the second and third electronic heat pump devices, the emitter 81 and the collector 82 are formed by a manufacturing method in which a thin film made of Si, Ti, Mo or the like is formed as a sacrificial layer on one electrode member, and the other electrode is laid on top of the sacrificial layer to form a three-layer structure. Then, the three-layer structure is cooled to preferably −100° C. to −150° C. to destroy the sacrificial layer, and finally two electrodes that would be the emitter 81 and the collector 82 are formed. It is to be noted that there is another manufacturing method in which Cd, Zn, Na, or K is used as the sacrificial layer material, and the sacrificial layer is heated and melted so as to obtain the two electrodes.
Then, the vacuum gap 83 is regulated to be 10 nm or less, more preferably, 5 nm or less, and a voltage is applied to both the electrodes to feed current, by which an electronic heat pump device capable of cooling the emitter 81 side while heating the collector 82 side is manufactured.
As shown in FIG. 42, the fourth electronic heat pump device has an emitter 91, a collector 92 and a dielectric 94 disposed in a vacuum gap 93 between the emitter 91 and the collector 92 (see JP 2002-540636 A). The dielectric 94 is made of a material containing Al2O3 or SiO2, which is formed into a spherical shape or a wire shape or is spread over the electrodes by sputtering, and becomes a barrier to maintain the spacing of the vacuum gap 93. Then, electronic filtering by the dielectric (barrier) 94 is performed to move electrons together with heat from the emitter 91.
However, the conventional electronic heat pump devices have the following problems.
In the Peltier device shown in FIG. 37, voltage application and current feeding causes heat absorption or heat generation between each of the semiconductors 51, 52 and the electrodes 53. However, since heat is generated at both ends of each of the semiconductors 51, 52, back flows of heat through the semiconductors 51, 52 occur as shown by arrow 50 to deteriorate thermal conversion efficiency, causing a problem that a specified cooling capability cannot be achieved without an increased power consumption.
Moreover, in the first electronic heat pump device shown in FIG. 39, it is necessary to support both the cathode 71 and the anode 72 for maintaining the vacuum gap 73 at a specified spacing. However, in this structure, the electrodes 71, 72 each are thermally in direct contact with the cooling target or the heating target, and so the cathode 71 and the anode 72 are warped by stress including the weights of the targets themselves and atmospheric pressure, which makes it difficult to maintain the specified spacing. Moreover, in the worst case, the cathode 71 and the anode 72 adhere to each other and fail to function as an electronic heat pump device.
Further, in the second electronic heat pump device shown in FIG. 40, in order to solve the problem of the first electronic heat pump device shown in FIG. 39, regulation of capacitance is performed in one electrode by a capacitance controller 88 using the piezoelectric element 86 so as to maintain the vacuum gap 83 at a specified distance. However, the gap regulation is performed based on measurement of capacitance through the piezoelectric element 86, and therefore during operation of the electronic heat pump device, heating of the collector 82 side causes the piezoelectric element 86 to have a temperature capacity change, which makes the capacitance of the emitter. 81 and the collector 82 imponderable, and thereby disables the vacuum gap 83 from maintaining a specified value. That is, it becomes impossible to maintain the vacuum gap 83 at a specified spacing. Further, at the midpoint of a heat transfer path from the collector 82 where heat generates to the second thermal conduction section 85, there is present a line that links the piezoelectric element 86 and the capacitance controller 88, which causes a considerable loss in heat transfer from the collector 82 to the second thermal conduction section 85.
Further, in the third electronic heat pump device shown in FIG. 41, in order to solve the problem concerning the vacuum gap 83 involving the capacitance in the second electronic heat pump device shown in FIG. 40, the capacitance is measured directly in the emitter 81 and the collector 82 and the piezoelectric element 86 is provided as a separate circuit, which performs full-time control so as to maintain the vacuum gap 83 to be a specified distance.
In this case, a gap regulator circuit made of the piezoelectric element 86 which offers full-time operation is required, which is considered to increase power consumption in a circuit unrelated to an original electronic heat pump device. Moreover, since individual electronic heat pump devices are controlled by the aforementioned circuit, it becomes difficult to develop a unitized structure using a plurality of electronic heat pump devices in consideration of the expansion of heat pump capacity. Further, at the midpoint of a heat transfer path from the collector 82 where heat generates to the second thermal conduction section 85, there is present a line that links the piezoelectric element 86 and the capacitance controller 88, which causes a considerable loss in heat transfer from the collector 82 to the second thermal conduction section 85.
Further, in the fourth electronic heat pump device shown in FIG. 42, it is difficult to dispose the dielectric 94 so as to have a constant area ratio to the emitter 91 and the collector 92. Further, it has been stated that the dielectric 94 is spread over the electrodes by sputtering, and electronic filtering is performed to move electrons together with heat. However, as with the Peltier device, a back flow of heat through the dielectric 94 occurs, thereby causing a problem of poor cooling efficiency and increased power consumption.